Reasons for using hydrogen as a fuel in vehicles – reducing the consumption of fossil fuels and the production of harmful emissions

It is expected that in the future, production of fossil fuels (mainly oil and natural gas) is will decline, and their prices will continue to rise. One alternative fuel to replace them could be hydrogen, as its reserves in water are almost inexhaustible.

The heat of combustion of hydrogen was noticed by natural scientists and technicians a long time ago, but its industrial use did not begin until the early 20th century, primarily for welding or as a hydrogenating and reducing agent. The first experiments with using hydrogen as a fuel for rocket engines started in the early 1950s and did not reach the implementation phase until the mid-1960s.

The main advantage of hydrogen as a fuel is its clean combustion. When hydrogen is used in internal combustion engines or in fuel cells, it produces thermal, mechanical, or electrical energy and a harmless byproduct: water. It does not produce any waste CO2 or other combustion by-products that result from the combustion of solid, liquid, or gaseous hydrocarbon fuels. CO2 is the main component of greenhouse gases, and the hydrogen economy aims primarily to limit their formation."

Hydrogen reserves in water are nearly inexhaustible. It has a high energy density per unit weight and can be transported and stored. From an environmental perspective, burning hydrogen is cleaner than burning fossil fuels, and produced water is not accompanied by toxic compounds or greenhouse gases.

On an industrial scale, hydrogen is produced on the one hand by petrochemical processes, including coal gasification (accounting for 90% of production), and through electrolysis of water. It is also an important byproduct or component of gases generated by refineries, coking plants, and electrochemical production based on aqueous solutions of inorganic acids or salts.

 

Hydrogen is a colorless, tasteless, and odorless gas and is the lightest of all gases.

Chemical formula: H2

CAS number: 1333-74-0

EC number: 215-605-7

UN number: 1049

Hydrogen is the simplest and most abundant element in the universe, accounting for about 75%. Although molecular hydrogen (H2) is rare on earth, it can be found bound in water and hydrocarbons.

However, its low density presents storage and distribution challenges.  As liquification is only possible only after cooling below the critical temperature of 33.15 K

The main objective of adopting hydrogen economy is to achieve climate neutrality by 2050.

The importance of the of hydrogen has been repeatedly emphasized in strategy documents for the Green Deal, including the "The Hydrogen Strategy for a Climate Neutral Europe".

 

Physical properties

Molecular weight: 2.02 g

Boiling point: -252.9 °C

Triple point: -259.2 °C

Critical temperature: -239.9 °C

Critical pressure: 12.8 atm

Gas density at 0 °C and 1 atm (air = 1): 0.089 g/l

Gas density at 25 °C and 1 atm (air = 1): 0.069 g/l

Auto-ignition temperature in air at 1 atm: 570 °C

Although hydrogen is relatively inactive at ambient temperature, it reacts with most other elements at elevated temperatures. For instance, hydrogen can reduce metal oxides at elevated temperatures. This reactivity at elevated temperatures is widely used in most industrial hydrogen installations outside the energy sector.

Therefore, hydrogen can be considered incompatible with oxidants such as air, oxygen, and halogens. For example, fluorine and hydrogen react at a temperature of 250 °C in the presence of impurities. Mixtures of chlorine and hydrogen are prone to explosion when exposed to light, and lithium burns in a hydrogen atmosphere.

Hydrogen is an extremely flammable gas and burns in air with a pale blue flame that is practically invisible in concentrations from 4 to 75% by volume under standard conditions.

Moreover, hydrogen is processed at elevated pressures. If there is a leak, the hydrogen causes an inverse Joule-Thompson effect, resulting in the escaping gas getting hot enough to ignite immediately. This increases the low minimum ignition energy of the flammable mixture of hydrogen and air, making it more sensitive to the probability of ignition compared to other flammable gases.

The likelihood of ignition is also higher compared to other flammable gases because the small size of the hydrogen molecule allows it to leak more easily through small holes. This property is the reason why equipment intended to contain hydrogen is sometimes tested for tightness with helium, an inert gas, as its molecule size is comparable to that of hydrogen.

Because hydrogen is lighter than air, the gas easily rises into the atmosphere, unlike propane, which remains at ground level, increasing the risk of explosion. Practice shows that hydrogen does not ignite in open air.

Therefore, the main danger associated with the use of hydrogen is the formation of flammable mixtures with air, which, when exposed to an ignition source, can lead to a fire or possibly a deflagration. The gap that a hydrogen flame can spread in is much narrower than most other gases, making it very difficult to design electric motors that are sufficiently "tough" for use in atmospheres where a flammable mixture of hydrogen and air may be present.